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Lancet. 2008 Jul 26;372(9635):314-20. doi: 10.1016/S0140-6736(08)61115-0.

Relation between HIV viral load and infectiousness: a model-based analysis.

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National Centre in HIV Epidemiology and Clinical Research, University of New South Wales, Sydney, NSW, Australia.

Erratum in

  • Lancet. 2008 Nov 22;372(9652):1808.



A consensus statement released on behalf of the Swiss Federal Commission for HIV/AIDS suggests that people receiving effective antiretroviral therapy-ie, those with undetectable plasma HIV RNA (<40 copies per mL)-are sexually non-infectious. We analysed the implications of this statement at a population level.


We used a simple mathematical model to estimate the cumulative risk of HIV transmission from effectively treated HIV-infected patients (HIV RNA <10 copies per mL) over a prolonged period. We investigated the risk of unprotected sexual transmission per act and cumulatively over many exposures, within couples initially discordant for HIV status.


Assuming that each couple had 100 sexual encounters per year, the cumulative probability of transmission to the serodiscordant partner each year is 0.0022 (uncertainty bounds 0.0008-0.0058) for female-to-male transmission, 0.0043 (0.0016-0.0115) for male-to-female transmission, and 0.043 (0.0159-0.1097) for male-to-male transmission. In a population of 10 000 serodiscordant partnerships, over 10 years the expected number of seroconversions would be 215 (80-564) for female-to-male transmission, 425 (159-1096) for male-to-female transmission, and 3524 (1477-6871) for male-to-male transmission, corresponding to an increase in incidence of four times compared with incidence under current rates of condom use.


Our analyses suggest that the risk of HIV transmission in heterosexual partnerships in the presence of effective treatment is low but non-zero and that the transmission risk in male homosexual partnerships is high over repeated exposures. If the claim of non-infectiousness in effectively treated patients was widely accepted, and condom use subsequently declined, then there is the potential for substantial increases in HIV incidence.


Australian Research Council.

[Indexed for MEDLINE]

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